1. Field of the Invention
The present invention relates to a damper device to be used mainly for mounting an engine.
2. Description of the Prior Art
As the damper device of that kind, there is known in the relevant art the construction which is disclosed in U.S. Pat. No. 4,159,091 to Le Salver et al.
The damper device disclosed is so constructed that an elastic rubber member is sandwiched between a mounting member to a vehicular body and a mounting member to an engine, that a main sealed chamber and an auxiliary chamber are formed therein such that both the former chamber and at least a portion of the latter chamber are charged with a liquid, and that such a partition as is made movable in the direction to join the two chambers and as has its movable range restricted is arranged to partition the main and auxiliary sealed chambers and is formed with an orifice.
In the damper device disclosed in that the above-mentioned U.S. Patent, since the partition separating the main and auxiliary sealed chambers is made movable, the dynamic spring constant in the vicinity of a high-frequency range (of 100 Hz) is far smaller than that of the device having its partition fixed. Thus, that damper device can have desired dynamic spring constant characteristics in the high-frequency range.
However, the flow of the liquid passing through the orifice becomes turbulent even under the condition in which the flow velocity of the liquid passing through the orifice not only for a large amplitude (of .+-.0.5 mm) in a low-frequency range (in the vicinity of 15 Hz) but also for a small amplitude (of .+-.0.05 mm) in a high-frequency range is considerably decreased. As a result, it has been found that the damping constants not only in the low-frequency range but also in the high-frequency range become large and accordingly that the vibration-isolation characteristics in the high-frequency range are not satisfactory.
It has also been found that the damping constant in the high-frequency range can be reduced in case that damping device is not formed with the orifice.
More specifically, if the circular orifice is removed from that damping device so that the liquid is made to pass through a slot-shaped passage formed between a partition and a surrounding wall thereof, the liquid flow passing in the high-frequency range is more liable to become laminar than that passing through the circular orifice. As a result, it has further been found the damping constant in the high-frequency range can be made far smaller than that in the case of the circular orifice if the whole effective area of the slot passage for the liquid is made the same as that of the circular orifice. In the low-frequency range, on the other hand, since the flow velocity of the liquid passing through the slot passage is far higher than that of the liquid in the high-frequency range, the liquid flow becomes turbulent similarly to that passing through the circular orifice. It has further been found that the damping constant is as high as that in the case of the circular orifice.
In view of the foregoing description, we, the inventors, have discovered that the cause for enlarging the damping constant in the high-frequency range is attributed to the circular orifice.